The invention relates to a fuel-air ratio controller for use in an internal combustion engine including a device for measuring the air quantity aspirated by the engine (air measuring member) and including a fuel metering system.
In order to maintain a low level of emission of toxic components from internal combustion engines, a favorable fuel ratio must be maintained. This is true in the same degree for conventional, externally ignited engines as for engines employing stratified charge or self-ignition.
In the known fuel metering systems used with internal combustion engines, the command variable for maintaining the fuel-air ratio is either the air quantity provided to the engine or the fuel quantity provided to the engine, and the required complementary substance, i.e., either fuel or air, respectively, is metered out in accordance with the common variable. Thus, it is customary, in externally ignited internal combustion engines, to use the butterfly throttle valve in the induction tube, which arbitrarily determines the air quantity aspirated by the engine, to generate the command variable. In order to maintain the desired fuel-air mixture, this changeable air quantity is measured and a corresponding fuel quantity is allotted to it. If the air quantity changes, then the fuel quantity also changes. Metering errors, for example, those occurring when jets become clogged, cannot be controlled in such "direct control systems", so that very rapid build-ups of toxic emissions can occur of which the operator of the internal combustion engine is unaware until the engine performs poorly. In particular, in engines employing intermittent injection, the air flow rate is measured by measuring the induction tube pressure. Thus, the air quantity is not measured directly, but is determined via the air pressure and this leads to corresponding errors in the associated fuel metering process.
In self-igniting internal combustion engines, it is generally the fuel quantity which is changed arbitrarily and air is aspirated by the engine as required. This type of internal combustion engine usually operates with a large surplus of air and this can also lead to undesirable toxic emissions, because the excess air causes a particularly hot combustion process with a high level of nitrogen oxide emissions.